It's beginning to look like the near-term technology for making diesels clean enough to meet 2010 emissions rules will involve urea.  Or perhaps we should say, MORE urea-Mercedes alone currently offers four diesel models in North America, including the E320 sedan, that currently rely on a urea-based emissions system.

You have probably heard that urea is a way of carrying ammonia, which can be used to catalyze NOx. Selective Catalyst Reduction (SCR) systems are now being developed that use urea to generate ammonia, which in turn cuts NOx.

As the dieselization of North America progresses as predicted, there's going to be a whole lot of urea going on. These SCR systems will be used on new cars and light trucks starting with 2008 models.  Which means that luxury car owners, truck drivers and soccer moms will need to fill up with urea every so often.

We wonder, where is all this urea going to come from, and how is everyone going to get it into their tanks?  Will there be a urea shortage? What will happen when your Blue Tec car or SUV runs out?  Does it quit on the spot?

Turns out that urea is a product already in mass production worldwide. An estimated 100 million tons are produced every year, most of which is used in fertilizer, especially water-soluble fertilizers. Urea is also used as an additive ingredient in cigarettes to enhance flavor, as a browning agent in pretzels, and in some facial cleansers and lotions. You have probably had it in your mouth already, since it is an ingredient in many tooth-whitening products. Urea is also a component of the chemicals included in ready-to-use cold compresses (first aid for sprains, etc).

Urea is a useful alternative to rock salt for melting ice on sidewalks and runways, since it does not attack steel the way salt will.

Last but not least, it is the active ingredient in AdBlue and other SCR systems. You might not think you need urea in your life, but probably, it already is.

It is produced commercially from ammonia and carbon dioxide.  Large quantities of carbon dioxide are produced during the manufacture of ammonia from coal or natural gas, which allows synthesis of urea. So there is plenty of it around already, and more can easily be made.

This is a good thing, because new clean diesels are going to need it. Recently the EPA released guidelines for cars that use urea in their SCR systems. The issue was that consumers might not choose to refill their urea tanks when they emptied, undercutting the effect of the SCR and possibly damaging the system, which is supposed to last at least 120,000 miles. Manufacturers, such as Mercedes, understandably horrified at the prospect of a car that could strand its owner, lobbied the EPA to develop a regulatory guideline they could live with. Fortunately, the EPA developed a more practical way of ensuring the clean diesel systems stay clean.

First, manufacturers will be required to have an instrument panel warning light that alerts the driver to low urea supply about 1,000 miles before the tank is empty. There will also be a warning that alerts if the wrong chemicals are used in the tank.

For those drivers who continue to ignore the warnings, the EPA recommends other driver inducements, such as an electronic system that limits the number of vehicle starts once urea reaches critically low levels.

Making urea refills convenient is being addressed by companies such as Benecor of Fenton, Michigan.  Benecor packages urea in totes, drums and bottles, and has recently developed a large-capacity, free-standing above-ground dispenser that could be placed in garages and gas stations on a widespread basis.  Could be, come 2010, you'll be seeing a lot of these.